Root Canal Vs Filling

A filling repairs a tooth damaged by decay that has not reached the nerve. A root canal treats a tooth when the soft tissue inside, called the pulp, becomes infected or inflamed. The right choice depends on how deep the damage goes.

6 min readMedically reviewed by MSD Clinical Editorial TeamLast updated June 15, 2026

Key Takeaways

A filling treats decay in the outer tooth, while a root canal treats infection inside it. The decision depends on whether the pulp, the soft tissue inside the tooth, is healthy or infected.^[7]
A root canal removes infected pulp and seals the canal. Dentists fill the cleaned canal with a sealing material, and the technique used can affect how completely it seals.^[4]
Most patients feel mild soreness after treatment, not severe pain. A meta-analysis of randomized trials compared postoperative pain across root canal filling techniques.^[3]
Endodontic treatment can sometimes darken a tooth over time. A cross-sectional study found that endodontic treatment is associated with tooth discoloration.^[5]
Dentists confirm whether you need a root canal with tests, not guesswork. A cold test checks the pulp's response, and X-rays or CBCT scans can reveal infection at the root tip.^[1]
Saving your natural teeth is often better than removing a damaged tooth. The American Association of Endodontists supports keeping natural teeth and normal chewing when possible.^[7]

Overview

This guide explains the difference between a root canal vs filling, when you need each one, and what to expect.

Both are common dental procedures, but they treat different stages of damage. A filling repairs a small hole in the hard outer tooth structure. A root canal procedure treats the soft tissue inside the tooth when decay or injury reaches the nerve. Both treat tooth decay, but at different points along the way.

Knowing how fillings and root canals differ helps you ask better questions at your appointment. Root canal therapy is a focus of endodontics, the dental specialty that treats the inside of the tooth. You can learn more on the endodontics page.

Key Information

The main difference is depth: a filling treats decay in the outer tooth, while a root canal treats infection deep inside.

When a Filling Is Enough

A filling is the right fix when tooth decay is small to moderate and has not reached the pulp. The dentist removes the decayed part of the tooth and rebuilds the lost tooth structure with a filling material. This stops the decay from spreading and protects the tooth from further damage. When the nerve is still healthy, the repair is often just a filling and nothing more.

When a Root Canal Is Needed

You may need a root canal when decay, a crack, or repeated dental work lets bacteria reach the pulp. The pulp is the soft tissue inside the tooth that holds nerves and blood vessels. Once the infected pulp cannot heal on its own, treatment becomes necessary.

A root canal requires removing the infected pulp, cleaning the canal, and sealing it. Signs of an infected pulp include lasting tooth pain, swelling near the tooth, or sharp pain when you bite down. Some teeth have no symptoms, so a dentist may find the problem on an X-ray.

How Dentists Tell the Difference

Dentists use tests to decide between fillings and root canals, not just a look. A cold test places a cold stimulus on the tooth to see how the pulp reacts. A healthy pulp feels the cold briefly. A pulp that reacts with lingering pain, or gives no response at all, may signal damage.

Imaging adds more detail. One 2025 study in the International Endodontic Journal compared an artificial intelligence platform with expert endodontists for spotting apical radiolucencies, dark spots that can signal infection, using CBCT scans as the benchmark.^[1] X-rays show how deep the decay reaches and whether infection sits at the root tip.

What to Know

Timing matters: treating a small cavity early may need a simple filling, while waiting can lead to a root canal.

Tooth decay grows over time. Catching it early often means a simpler, lower-cost repair. People of any age can need fillings or root canals, including older adults whose teeth show years of wear. Children with adult teeth can also need root canal treatment, though the approach differs for teeth that are still developing.

To prepare, tell your dentist about symptoms such as tooth pain, sensitivity, or swelling. Share your full health history and any medicines you take. Most root canal treatment can be done with local anesthetic, and you can usually drive yourself home afterward.

Daily care lowers your risk of deep decay and infection. Brushing twice a day and flossing help protect against tooth decay, and the American Dental Association offers patient guidance on prevention.^[8] If you plan orthodontic treatment, tell your provider about any root-filled teeth. A systematic review and meta-analysis examined external apical root resorption, a shortening of the root tip, in root-filled teeth compared with teeth that still have a living pulp during orthodontic movement.^[2]

What to Expect

During a root canal procedure, the dentist numbs the tooth, removes the infected pulp, cleans the canals, and seals them.

Sealing the canal well is what protects the tooth long term. The step of filling the canal is called obturation. A systematic review of micro-CT studies compared cold lateral condensation, an older packing method, with thermoplastic techniques that warm the filling material so it flows into the canal.^[4] Both aim to fill the space completely and leave no gaps for bacteria.

Some soreness after treatment is normal. A systematic review and meta-analysis of randomized controlled trials looked at postoperative pain after root canal filling, comparing bioceramic materials with traditional techniques.^[3] In many cases, discomfort is mild and eases within a few days, and over-the-counter pain relievers usually help. Research on endodontic programs has also studied how to improve the success of root canal treatment in everyday practice.^[6]

A filling visit is shorter and simpler. The dentist numbs the tooth, removes the decay, and places the filling, often in one visit. You may feel some sensitivity for a few days, which typically fades.

The dentist numbs the area with local anesthetic so you stay comfortable.
A small opening is made in the top of the tooth to reach the pulp.
The infected pulp is removed, and the canals are cleaned and shaped.
The cleaned canals are filled and sealed with a filling material.
A crown or permanent filling restores the treated tooth so you can chew normally.

Cost Factors

A filling usually costs less than a root canal, because it is a simpler procedure with fewer steps.

Costs vary by location, provider, and case complexity. A molar with several canals usually costs more to treat than a front tooth with a single canal. The filling material used and whether you need a crown afterward also change the total.

Many dental insurance plans cover part of both fillings and root canals, but limits differ. Ask your provider for a written estimate before treatment, and check what your plan pays. Keeping your natural tooth can cost less over time than removing it and replacing it, and the American Association of Endodontists supports saving the natural tooth when possible.^[7]

When to See a Specialist

See an endodontist, a specialist in root canal therapy, when a tooth has complex canals or pain that is hard to diagnose.

A general dentist handles most fillings and many of these procedures. Consider asking for a referral to an endodontist in these cases:

Endodontists use magnification and advanced imaging such as CBCT scans to find and treat problems inside the tooth.^[1] Detecting infection at the root tip early helps protect the tooth. If your dentist is unsure whether you need a root canal or a filling, a specialist can confirm the diagnosis.

Your tooth has curved or extra canals that are hard to reach.
A previous root canal did not heal and needs retreatment.
You have lasting tooth pain that standard tests cannot explain.
The infected tooth is a molar with several canals.
You have a cracked tooth or a tooth injury from an accident.

Find a Specialist

Tooth pain or a deep cavity does not always require treatment, and the right answer starts with an exam. If you want a clear diagnosis or a second opinion, connect with an endodontist near you through the endodontics page. A specialist can tell you whether your tooth needs a root canal, just a filling, or another option, and explain the choice in plain terms.

Search Endodontists in Your Area

Frequently Asked Questions

Is a root canal worse than a filling?

The procedure takes longer than a filling because it treats infection inside the tooth, not just surface decay. Modern treatment is done with local anesthetic, so most patients feel little pain during the visit. Soreness afterward is usually short-term, and a meta-analysis of randomized trials has compared postoperative pain across different filling techniques.^[3]

How do I know if I need a root canal or a filling?

Your dentist decides based on how deep the damage goes. If decay has not reached the pulp, you likely need a filling. If the pulp is infected or inflamed, a root canal is the right treatment. A cold test and X-rays help confirm which one you need.^[1]

Can a filling fix an infected tooth?

No. A filling repairs decay in the outer tooth structure, but it cannot treat infected pulp inside the tooth. Once bacteria reach the soft tissue inside, a root canal procedure is needed to remove the infection and seal the canal.^[7]

Why does a root canal cost more than a filling?

It is more complex and takes more time than a filling. It often needs a crown afterward to protect the treated tooth, which adds to the cost. Costs vary by location, provider, and case complexity.

Does a root canal turn the tooth black?

A treated tooth can sometimes darken over time. A cross-sectional study found that endodontic treatment is associated with tooth discoloration.^[5] If a front tooth changes color, a dentist can often whiten it or place a crown or veneer to restore its look.

How long does a root canal take compared to a filling?

A filling usually takes one short visit. The treatment may take one or two longer visits, depending on the tooth and the number of canals. Back molars with several canals take more time than a single-canal front tooth.